The present invention relates to a new and improved construction of roller apron framework or strand guide framework for supporting a partially solidified strand in a continuous casting installation, comprising at least two guide roller pairs which follow one another in the direction of travel of the strand, the guide roller pairs being provided with supporting rollers, the lengthwise axes of the supporting rollers being arranged with respect to the lengthwise axes of the guide rollers approximately in a plane located transversely with respect to the axis of the direction of travel of the strand and wherein the framework is equipped with secondary cooling means or devices.
The guide rollers of continuous casting installations during each rotation are exposed to a high mechanical alternating load owing to the ferrostatic pressure which acts upon the shell or skin of the strand and, in the case of slab continuous casting installations, can amount to more than 100 tons per roller. An additional loading of the rollers is brought about owing to the shock-like temperature increase of the roller surface during each contact with the hot strand. This mechanical and thermal loading requires, depending upon the strength of the roller material, a certain roller diameter from which, while taking into account the secondary cooling device, there can be derived a certain roller spacing and thus the size of the unsupported surfaces. The alternate dependency between the permissible roller loading by the ferrostatic pressure, the strand width, the frozen shell thickness, the roller diameter and the spacing of successive rollers, in the case of large cast shapes limits the casting speed since there must be avoided damaging bulging and breakouts. Strands with widths of, for instance, 2.5 to 3 meters can not be rationally cast with the aforementioned devices.
In order to be able to maintain a small roller spacing between two successive guide rollers, it is known to the art to construct such rollers as multiple-part components and to support the same at a number of locations by bearings. Such roller bearings which are arranged directly over the hot strand are, however, exposed to the thermal radiation of the strand and in the case of insufficient strand cooling at the region of the bearings are strongly endangered owing to overheating and seizing.
Furthermore, it is known to the art in straightening drivers of curved continuous casting installations to provide the lower rollers at the tangent point and the reaction rollers which take-up the straightening forces with supporting or support rollers. Such support rollers which are arranged individually in straightening machines can be freely selected as to their diameter because the guide rollers neighboring the straightening rollers and reaction rollers are not equipped with support rollers.
There is also known to the art a strand guide arrangement or roller apron for continuous casting installations in which the driving rollers are supported by equally strong supporting rollers continuously at their spherical portions or crowns. For such roller arrangement the drive rollers and the support rollers which are in contact therewith are equally markedly bent-through under the action of the ferrostatic pressure owing to the same loading. The bending-through and mechanical loads or stresses in the drive rollers which are located in contact with the strand, with this arrangement, only can be reduced a relatively small amount. Since such drive rollers are additionally exposed to the alternating thermal loads, the entire or total loading of the drive rollers is considerably greater than that of the support rollers. An increase of the drive roller diameter automatically brings about a larger undesired roller spacing.